Fatigue is a common clinical symptom in persons with neuromotor disorders, many of whom have a concomitant dysarthria. To track fatigue-related changes with treatment or disease progression, an objective measure is needed to quantify fatigue. The long-term objectives of this research are to validate a clinical assessment of tongue fatigue and to examine the role of tongue fatigue in disordered speech. A noninvasive, nonaversive physiologic assessment technique has been designed and preliminarily tested to reflect the sense of effort associated with fatigue. The first specific aim is to use this technique to test individuals with Parkinson?s disease (PD), amyotrophic lateral sclerosis (ALS), and a group of sex- and age-matched, neurologically normal, control subjects. The benefit of this line of research is to provide a simple objective assessment of fatigue. According to the clinical literature, fatigue can exacerbate dysarthria; however, data are not available to substantiate this claim. The second specific aim of this research, therefore, tests the assumption that speech is more susceptible to fatigue in persons with dysarthria than in normal speakers. The study attempts to induce acute tongue fatigue with speech-like tongue exercises in the same groups of subjects (ALS, PD, neurologically normal) and to demonstrate effects on tongue function. The exercise consists of fast syllable repetitions involving lingual targets and movements. Tongue fatigue, indicated by the fatigue measure tested under Aim 1, is expected after the tongue exercises in the disordered groups. As a control for the potential effects of overall lassitude and reduced motivation, the subjects will perform the task with the hand before and after the speech-like exercises as well; no difference is anticipated. Furthermore, functional effects will be examined by comparing speech produced before and after the tongue exercises. This aim will provide evidence to support the clinical relevance of the exacerbation of dysarthria by fatigue and further validate the constant-effort technique as an indicator of fatigue.